Dynamic balancing system for rotating structures



center shifts in United States Patent O pany ,of France lFiled Feb. 19,1962Ser. No. 174,id Claims priority, application France Feb. 2S, i961 vSClaims. (Cl. i4-575) This invention relates to .systems for dynamicallybalancing rotating mechanical members, a problem that arises inconnection with any type of high-speed rotary machinery. Taking as an.example the case of a highspeed revolving grinding wheel in a grindingor rectifying machine, the center of gravity of the wheel is liable toshift slightly off-center with time because of irregularities in wearcoupled with minor non-unformities in the density of vthe wheelmaterial, and/or in the distribution of moisture in the pores of thewheel. At the high `:angular speeds involved, even very small offthecenter of gravity can result in the of large centrifugal forces liableto cause development heavy rea breakdown of the grinding wheel or othervolving part concerned.

It has already been proposed to provide automatic dynamic rebalancingsystems comprising essentially an annular recess filled with oil, forinstance having the shape of a tore, formed in a member carried by ashaft and concentric to said shaft, this recess being divided byseparation means in a certain number of chambers (usually 3 arcuatechambers extending each along 60, while said separation means extendeach along the same arcuate distance). ln each of said chambers amovable mass is located, said mass being free to be displaceable alongthe wall of the chamber in which it is located, the chamberscommunicating with each other by passages extending through saidseparation means. The 3 passages above are connected respectively to 3ducts provided in the shaft and opening radially in the oil lm of thebearing, each of the pressure receiving openings being at 120 in respectto any one of the other openings. The pressure differentials created inthe oil film of the bearing by an unbalance are transmitted to thecorresponding chamber, so that the movable masses are supposed to move'in respect to each other so as to compensate the unbalancing effect.

Unfortunately, the experience has proved that systems of the type aboveare not able to ensure the proper feeding of oil with the clearance.provided in usual oil bearings due to the unsuliicient output of oilsupplied by the oil ilrn of the bearing, said output being unsufiicientfor rapidly acting on the compensating masses in order to displace themaccording to the pressure variations. To increase said output it wouldhave been necessary to increase considerably the pressure differentialsacting on the pressure receiving openings of the ducts mentioned aboveand located at 120 in respect to each other (which would actually meanthe increase of the value of the compensating signal). This result couldonly be obtained .by an increase of the section of the clearance whichwould not be compatible with a proper operation of the rotating system.In addition, the low output mentioned above may induce to reduce thevolume of the chambers (which could not be extended beyond 60), so thatthe limited displacement of the balancing masses did not permit tocompensate the balancing forces when these forces became high enough tobe objectionable.

It is an object of this invention to provide an improved automaticdynamic re-balancing system for rotating mechanical members, which willhave better performance characteristics than similar systems heretoforePatented Nov. 24, 1964 ICC available; objects are to increase theresponse rate of such systems and -to ensure a 4more uniformly effectivebalancing action throughout the rotation of lthe rotary member.

In fulfilling these objects of the invention, there is provided in adynamic balancing system of the type above defined, a plurality ofcircumferentially spaced recesses formed in the periphery of therotating shaft within its bearing said recesses being equal in number tothe plurality of movable elements, passage means connecting each of saidrecesses with a corresponding one of .the balancing chambers, and meansfor supplying fluid .under pressure to veach recess and, consequently,to the corresponding 'interconnected balancing chamber. So, a body ofiiuid under pressure is interposed between said shaft and bearing, inthe zone including said recesses, said body supporting at leastpartially said shaft in the manner rknown in liuid type bearings.

In other terms, a bearing of the uid type combined with a balancingsystem permits to solve the diiiicult problem of feeding the annularrecess practically, because it permits `both to vary in the desiredmanner the output vof the iiuid and the `value of the pressuredifferentials supplying the compensating signal, this type of bearingbeing unaffected when mechanical clearances are relatively high, whichagain is due to the fact that the shaft is completely floating in theiluid under pressure without .ever contacting ,the stationary mechanicalparts.

`continutnls around the circumference thereof so `las to permit fully4uninhibited flow of fluid and transmission of pressure variationsyaround the raceway for producing the compensatory shiftingdisplacements of the movable elements along their arcuate path.

According to the invention, vabutments are provided inside the annularrecess to positively limit the displacement .of each compensating massso that no separation means are necessary and a continuous annularrecess takes place of the known arcuate chambers of a reduced length. Itis also an object to provide an improved .construction o'f the movablebalancing elements, which will ensure their smooth, free-floating,self-lubricated displacement along the continuous annular raceway insealing engagement with the walls thereof, while rendering themanufacture of such elements simple and inexpensive.

It is still another object of the invention to supply iiuid underpressure in parallel to each sustentation recess and correspondingbalancing chamber.

The above and further objects and advantages of the invention as well asthe novel features thereof will appear from the description to follow,in which an exemplary embodiment yof the improved dynamic balancingsystem is disclosed for purposes of illustration but not of limitationwith reference to the accompanying diagrammatic drawings, wherein:

FIG. l is a view of the improved apparatus in axial section;

FIGS. 2 and 3 are cross sectional views respectively on the planesdesignated Il--ll Aand Ill- III in FIG. l.

As shown an annular member 1 shown as a cylindrical member is secured ona shaft 2 for rotation therewith. Shaft 2 is rotatably mounted within abore in a smooth bea-ring member 3 by way of a fluid bearing laterdescribed. The shaft is here shown as being horizontal and the annularpart 1 is mounted on an end of the shaft by way of a rigid assemblygenerally designated 4 and providing a housing within it Vfor the activeportion of a dynamic balancing or compensating system presentlydescribed. The assembly 4 comprises a pair of parallel spaced iianges 5and 6 and a spacer ring 7 positioned between said flanges adjacent theradially outer surfaces thereof, said fianges and ring being suitablysecured by means not shown within the central bore of annular member 1.The assembly 4 is held in firm engagement against a shoulder il providedon shaft 2 by means such as a retainer nut 9 screwed on a threaded endpart of the shaft.

There is thus defined within the assembly 4, internally of flanges 5 and6 and ring 7 a continuous annular space of rectangular cross section.Disposed in this annular space or raceway are three movable reactionelements, preferably in the form of generally cylindrical rollers 11,12, 13. The rollers are so dimensioned that they are freely displaceablealong arcuate paths within the raceway while being at all times retainedin positions such that their axes are parallel to the axis of the shaft2. For this purpose the diameter of each roller is just slightlysmaller, e.g. by an amount of the order of 0.02 mm., than the differencein radius between ring 7 and shaft 2, and the length of each roller isjust slightly smaller, say

by about the same amount of 0.02 mm., than the axial spacing between theinner faces of flanges 5 and 6.

The three rollers 11, 12, 13 define, in the continuous raceway, threecompensating or balancing chambers 17, 18, 19. As will be apparent laterthe volumes of the three chambers are variable with the relativepositions of the three rollers round the raceway. However, means such asstops 51, 52, 53 projecting from the inner periphery of ring 7 at 120degree spacings therearound, are provided for positively limiting thearcuate displacements of the three rollers to arcs such that thepositions of the three chambers cannot wander unrestrainedly around thecircumference of the shaft for reasons that will later appear. Topromote smooth frictionless displacement of the rollers along theirarcuate paths, the opposite end faces of each roller are interconnectedby a number of axial passages, herein shown as a central passage 57 andfour passages 58 spaced around the circumference of the roller andconnecting at their opposite ends with annular grooves 59 formed in theroller end faces.

Formed in the peripheral surface of shaft 2 within the axial extent ofbearing sleeve 3 are three arcuate sustentation recesses 21, 22, 23 (seeFIG. 3) which are of equal arcuate extent and are separated by equalarcuate distances. In operation fluid under pressure is maintained inthe three recesses through means presentlydescribed. Fluid flowing outof the recesses is collected by three longitudinal grooves 31, 32, 33formed in the periphery of shaft 2 intermediate the recesses as shown inFIG. 3, said grooves connecting at their opposite ends with a pair ofcircumferential channels 35 and 36 formed in the shaft beyond the endsof the recesses (see FIG. 1). The channels 3S, 36 communicate withregistering channels 37, 3S formed in the inner periphery of sleeve 3from which the fluid is returned to a sump or exhaust.

Means are provided for supplying uid under pressure` in parallel to eachof the balancing chambers 17, 18, 19 and a related one of the shaftrecesses 21, 22, 23. As shown, a radial inlet passage 41 formed in thebearing sleeve 3 is adapted to be externally connected with a pressuresource of said fluid, e.g. oil. The passage 41 delivers into acircumferential inlet manifold channel 42 formed in the inner surface ofsleeve 3. Two or more radial passages 43 formed in shaft 2 connect thecircumferential inlet manifold 42 with an axial bore 44 formed throughthe shaft 2. The outer end of bore 44 is adapted to be sealed with ascrew plug as indicated on the left of FIG. 1. Also bored into the shaftaround the axial passage 44 are three longitudinal, angularly spacedpassages 26. Each of the passages 26 is connected near one end by way ofa radial port 46 with the axial passage 44. Further, each passage 26 isconnected'by a radial passage 25 with a related point of the continuousannular raceway, the three passages 25 being angularly equispaced andbeing positioned opposite to the respective stops 51, 52, 53 (see FIG.2) so as to deliver into each of the three balancing chambers 17, 13,19, respectively regardless ofthe positions of the rollers. Moreover,each longitudinal passage 26 connects by another radial passage 27 withthe center of a related one of the recesses 21, 22, 23.

interposed in each longitudinal passage 26 between its connection 46with the central bore 44 and its connection 25 with the raceway is aninsert 47 providing a calibrated restricted orifice. Optionally anothercalibrated insert 30 is shown as inserted into each of the passages 25.

1t will be evident from the description above that pressure fluid frominlet 41 flowing through inlet manifold 42, radial passages 43 and axialbore 44, is thence delivered in parallel, through a restriction such as47, to each of the three balancing chambers 17, 18, 19 and the relatedshaft recesses 21, 22, 23. Effluent fluid from the shaft recesses isreturned to the sump via grooves 31, 32, 33, channels 37 and 38 and theoutlet shown.

The system operates as follows. Assuming the rotating assemblycomprising shaft 2 and the annular part 1 (which be it noted may standfor any complex revolving assembly) is perfectly centered dynamically,i.e. its center of gravity is positioned accurately on the rotationalaxis of shaft 2, then the thickness of the fluid film between theadjacent surfaces of shaft 2 and bearing sleeve 3 is continually uniformall around the circumference of the shaft throughout each shaftrevolution (disregarding for the time being the minor and constanteffect of gravity present when the rotational axis is horizontal as hereshown). The uid pressure in all three recesses 21, 22, 23 and hence inall three balancing chambers 17, 13, 19 con nected thereto, is hencecontinually the same. Because of the equal pressures in chambers 17, 18,19, the three rollers 11, 12, 13 assume equi-angular positions along theraceway as shown'.

Assume now that an unbalance mass is present at some point in therevolving assembly, due to some uncontrollable cause. Such an unbalancemass has here been symbolically indicated as a small additional weight Battached to a point of annular part 1, specifically adjacent the stop 51marking the center of balancing chamber 17. The unbalance will generatea centrifugal force which throughout each revolution tends to press therecess 21 of the shaft into tight engagement with the inner surface ofbearing 3, so that the fluid film thickness is reduced in thecorresponding shaft area and the pressure in recess 21 becomes greaterwhile the pressure in the other two recesses Z2, 23 growscorrespondingly lower. Similar pressure variations are reflected in thethree balancing chambers 17, 18, 19, respectively connected with therecesses 21, 22, 23, so that the pressure in chamber 17 is increased andthat in chambers 18 and 19 correspondingly decreased. Hence the rollers12, 13 defining chamber 17 are urged away from each other along theraceway, increasing the volume of chamber 17 and reducing the volumes ofchambers 18 and 19. This outward motion of rollers 12, 13 towards roller11 creates an unbalance reverse from that produced by the mass B, andwhen the roller displacement has been sufficient to offset the initialunbalance so that the resulting centrifugal force is zero and the shaftis revolving in a centered condition in its bearing, the pressures inthe three shaft recesses 21, 22, 23 and hence in the three chambers 17,18, 19 are equalized so that the rollers 12 and 13 remain relativelystationary in their displaced positions. This condition will last solong as the initial unbalance remains unchanged in amount and in phase(or angular position). Should such a change in amount and/ or in phaseoccur however, a sequence of events generally similar to that describedwill ensue, and the configuration of the three rollers around theraceway will undergo another shift to meet the changed condition landrestore the dynamically zbalanced, lcentered, condition of the shaft.

It is found in practice that the `"system described accomplishes apermanent and vcontinual compensation of a dynamic unbalance with veryrapid response, a result attributable in part -to the large ow `of fluidand to the high pressure under which the fluid is delivered in a iiuidbearing, as well as to the direct supply of fluid in parallel to eachshaft recess and balancing chamber, 'by way of a common restrictedorifice 47. This parallel supply of fluid is found to result insubstantially improved performance characteristics over what is obtainedwith a serial supply of iluid through the fluid film of the bearing tothe balancing chambers as i-n certain prior systems of the class towhich the invention is directed. Moreover, since the bearing recesses21, 22, 23 are formed in the shaft and hence revolved bodily with therotating assembly, accurate compensation is had continuously throughoutevery revolution.

As earlier noted the auxiliary restricted orifices such as 30 shown inthe connecting passages 25 may usually be omitted with good results whendesired to obtain maximum response speed of the rebalancing system.However, in some cases the insertion of the orifices 30 may be desirablein order to introduce some damping in the response characteristic. Thismay be especially useful in the case of a substantial gravity forcecomponent being present in the system, such as in the horizontal shaftsystem shown, since such a constant gravity component tends to inducecyclic pressure variations in the balancing chambers as the shaftrotates. Such cyclic pressure variations do not per se tend to producerelative shifting of the balancing rollers, since the mean values of thepressures remain constant. Moreover, normal damping due to the shear ofthe fluid through the various restricted passages in the fluid flowcircuit, including the passages around the rollers, usually suiice todampen out to a substantial extent the said cyclic variations. However,especially in the case of a lowspeed, heavyweight, horizontally mountedrevolving assembly, the use of the optional restricted inserts 30 mayprove desirable for further damping out any residual vibrations.

The balancing section of the system including the continuous annularraceway or channel containing the plurality of, preferably three,balancing elements in the form of perforate rollers, in combination withthe stop means 51, 52, 53 which positively limit the arcuatedisplacements of the rollers, as shown and described above, is highlyadvantageous for several reasons. While being simple and inexpensive toconstruct and assemble, the continuous annular channel ensures optimaltransmission of pressure variations through the body of uid containedtherein and hence optimal response to an unbalance; also the availablelength of displacement of the movable elements is increased for givenover-all dimensions. At the same time, the stops positively prevent thestraying of the balancing chambers all around the annular channel, whichwould otherwise result in incorrect operation since each balancingchamber 17, 18, 19 would then be liable to communicate with the wnongshaft recesses 21, 22, 23; said stops however do not substantiallyinterfere with the continuous character of the annular raceway in regardto the transmission of pressure forces. The cylindrical shape of thebalancing elements 1l, 12, 13 makes them easy to machine to therequisite tolerances and the axial perforations through the elementsensure pressure balance between the opposite ends thereof as well as aself-lubricating effect conducive t-o smooth floating displacement ofthe rollers around the raceway to effect the desired compensatingshifts.

What is claimed is:

1. The combination with a revolving assembly having a shaft rotatable inat least one bearing, of dynamic balancing means for said assemblycomprising a plurality of chambers, equi-angularly disposed rat theperiphery f of .said .shaft between said shaft and said :bearings,raceway means .defined :said assembly coaxially ,sur/rounding .saidshaft; a plurality of balancing-elements positioned in the raceway fordisplacement along arcuate paths .therein and defining .a plurality ofspaces between said elements, equal in number to said chambers; passagek.means connecting each .chamber with a related space, ,and

means for supplying fluid under pressure to .said passage means, saidfluid under pressure supporting at least partially said shaft; whereby apressure change occurring in any one of said chambers due to dynamicunbalance of the revolving assembly will induce a compensatory shift inthe relative position of said elements.

2. The combination with a revolving assembly having a shaft rotatable ina bearing surface, of dynamic balancing means comprising a plurality ofequi-angularly disposed chambers recessed in the shaft peripherysurrounded by said bearing surface; raceway means defined in saidassembly and coaxially surrounding the shaft; a plurality of balancingelements in the raceway displaceable along arcuate paths therein anddefining a plurality of spaces between said elements equal in number tosaid chambers; a passageway connecting each chamber with a relatedspace, fluid supply passage means formed through said bearing surfaceand other passage means formed through said shaft and communicating withsaid supply passage means; a plurality of restricted calibrated orificesconnecting said other passage means with each of said passageways forsupplying pressure fluid in parallel to all pairs of interconnectedspaces and chambers; and uid return passage means formed in said bearingsurface and communicating with said chambers.

3. In combination with a revolving assembly including a shaft, a bearingfor supporting said shaft with a clearance space therebetween, saidshaft having a bearing surface formed with a plurality ofcircumferentially spaced recesses, means defining in said assembly acontinuous annular raceway coaxially surrounding the shaft; a pluralityof balancing elements in the raceway displaceable along arcuate pathstherein and defining a plurality of spaces between said. elements; thenumber of said spaces being equal to the number of said recesses,angularly equispaced stop means positioned in said raceway for limitingthe arcuate paths of travel of said elements and thereby preserving therelative disposition of said spaces without substantially restrictingthe flow section of the raceway; a duct connecting each of said spaceswith one of said recesses, respectively, and means for conducting iluidunder pressure separately to each of said ducts.

4. The combination claimed in claim 3, wherein said ducts include eachan axially extending portion formed in said shaft, said portions openinginto said raceway at angularly equispaced points substantially radiallyaligned with said stop means.

5. In combination with a revolving assembly including a shaft, a bearingfor supporting said shaft with a clearance space therebetween, saidshaft having a bearing surface formed with a plurality ofcircumferentially spaced recesses, means defining in said assembly acontinuous annular raceway coaxially surrounding the shaft; a pluralityof cylindrical elements in the raceway positioned with their axesparallel to the shaft axis and displaceable along arcuate paths in theraceway in substantially fluid-sealing freely-displaceable relationshipwith the walls thereof to define with said walls a plurality of arcuatespaces of variable volume; the number of said spaces being equal to thenumber of said recesses, angular- 1y equispaced stops in the racewaylimiting the arcuate paths of travel of said elements and therebypreserving the relative disposition of the spaces defined between saidelements Without substantially restricting the flow section of theraceway; and duct means connecting each of said spaces with one of saidrecesses, respectively, and

means for conducting7 uid under pressure separately 8. The combinationclaimed in claim 2, wherein said to each of said duct means. fluidreturn passage means include passages recessed in 6. The combinationclaimed in claim 5, wherein said the shaft periphery parallel to theshaft axis and interelements have passages formed therethrough parallelto mediate each pair of adjacent first chambers. the axis of the elementand interconnecting the opposite 5 end faces there@ References Cited nthe tile of this patent 7. The combination claimed in claim 2, furtherinclud- UNITED STATES PATENTS ing a restricted calibrated oriceinterposed in the con- 2 659 243 Darrieus Nov 17 1953 nectlon from eachof sald passageways to the related 2,778,243 Darrieus Jan. 22. 1957space in the raceway.

UNITED STATES PATENT OFFICE CERTIFICATE OE CORRECTION Patent No 3 ,158,039 November 24, 1964 Paul Favrot It is hereby certified that errorappears in the above numbered p'atent requiring correction and that thesaid Letters Patent should read as corrected below.

and in the heading to the In the grant, 1ines Z and 12,

for "Landis printed specification, line 5, name of assignee, GendronS.A." each occurrence Signed and sealed this 20th day of July 1965.

(SEAL) Attest:

EDWARD J. BRENNER Commissioner of Patents ERNEST W. SWIDER AitestingOfficer

1. THE COMBINATION WITH A REVOLVING ASSEMBLY HAVING A SHAFT ROTATABLE INAT LEAST ONE BEARING, OF DYNAMIC BALANCING MEANS FOR SAID ASSEMBLYCOMPRISING A PLURALITY OF CHAMBERS, EQUI-ANGULARLY DISPOSED AT THEPERIPHERY OF SAID SHAFT BETWEEN SAID SHAFT AND SAID BEARING, RACEWAYMEANS DEFINED IN SAID ASSEMBLY COAXIALLY SURROUNDING SAID SHAFT; APLURALITY OF BALANCING ELEMENTS POSITIONED IN THE RACEWAY FORDISPLACEMENT ALONG ARCUATE PATHS THEREIN AND DEFINING A PLURALITY OFSPACES BETWEEN SAID ELEMENTS, EQUAL IN NUMBER TO SAID CHAMBERS; PASSAGEMEANS CONNECTING EACH CHAMBER WITH A RELATED SPACE, AND MEANS FORSUPPLYING FLUID UNDER PRESSURE TO SAID PASSAGE MEANS, SAID FLUID UNDERPRESSURE SUPPORTING AT LEAST PARTIALLY SAID SHAFT; WHEREBY A PRESSURECHANGE OCCURING IN ANY ONE OF SAID CHAMBERS DUE TO DYNAMIC UNBALANCE OFTHE REVOLVING ASSEMBLY WILL INDUCE A COMPENSATORY SHIFT IN THE RELATIVEPOSITION OF SAID ELEMENTS.